The existence of both optical and sub-THz nanomechanical resonances in the same laser microcavity results in strong photon-phonon interaction, and may be explored for the ultrafast control of vertical lasers. In the talk the experiments involving the injection of picosecond strain pulses into optically and electrically pumped vertical lasers, and monitoring of the modulated output laser intensity will be discussed. The results of three recent experiments will be presented:
• In the experiments with an optically pumped quantum dot laser, an increase of the lasing output induced by strain pulses by two orders of magnitude has been observed on a picosecond time scale. Such strong and ultrafast increase is due to the inhomogeneous quantum dot ensemble with a spectral broadening much larger than the optical cavity mode width. Thus, the optical resonance required for lasing is achieved for a tiny dot fraction only while non-resonant dots store optical excitation for long time. The strain pulse brings “non-resonant” quantum dots into the resonance with the cavity mode and the stored energy releases almost simultaneously in a form of the intense laser pulses.
• Experiments with electrically pumped micropillar lasers show the modulation of the emission wavelength on the frequencies equal to the resonant GHz nanomechanical modes of the micropillar.
• Experiments with a quantum well vertical laser showed intensity modulation with the mechanical resonance frequencies (20-40 GHz) of the optomechanical nanoresonator.
Prospective application for nanophotonics are discussed.
In the past decade, sound amplification by the stimulated emission of (acoustic phonon) radiation (saser) devices for generating coherent terahertz (THz) acoustic waves have been demonstrated [1 – 3]. The devices exploit the electron-phonon interactions in periodic semiconductor nanostructures known as superlattices (SLs) to amplify acoustic phonons. In addition, the particular acoustic properties of SLs can be exploited to make mirrors and cavities for THz phonons. Thus SLs can provide the two essential elements of a saser: the acoustic gain medium and the acoustic cavity.
In this presentation I will describe experimental studies of the THz phonon dynamics in a weakly-coupled GaAs/AlAs saser SL, which is DC electrically biased into the Wannier-Stark regime. Picoseconds-duration pulses of coherent THz acoustic phonons were generated using pump light pulses from a femtosecond laser and injected into the SL device. These phonon pulses seeded the saser cavity modes at about 220 and 440 GHz, which were amplified within the device. The phonons were detected using two methods: reflection of femtosecond probe light pulses, in a conventional pump-probe arrangement, and through the transient electrical response of the device itself.
When the DC bias conditions for saser were achieved in the device, the amplitude and lifetime of the seeded modes were both increased, analogous to the threshold and spectral line narrowing effects seen in laser devices.
[1] R P Beardsley et al., Phys. Rev. Lett. 104, 085501 (2010).
[2] W Maryam et al., Nature Communications 4:2184 (2013).
[3] K Shinokita et al., Phys. Rev. Lett. 116, 075504 (2016).
Spin-lattice coupling is one of the most prominent interactions mediating response of spin ensemble to ultrafast optical excitation. Here we exploit optically generated coherent and incoherent phonons to drive coherent spin dynamics, i.e. precession, in thin films of magnetostrictive metal Galfenol. We demonstrate unambiguously that coherent phonons, also seen as dynamical strain generated due to picosecond lattice temperature raise, give raise to magnetic anisotropy changes of the optically excited magnetic _lm; and this contribution may be comparable to or even dominate over the contribution from the temperature increase itself, considered as incoherent phonons.
We use the internal picosecond strain pulses to control the electron energy in a semiconductor quantum well. For
generating the strain pulse a 100 nm thick metal transducer was hit by intense laser pulse and a strain pulse with duration
~10 ps and amplitude up to 0.1% was injected into a GaAs substrate. This strain pulse travels strongly directed through
the crystal towards the quantum well generating at each momentary position a "nano-earthquake". When the quantum
well is hit by this "earth quake", the exciton resonance is shifted on a value up to 10 meV on a ps time scale.
We demonstrate ultrafast shifting of a photonic stop band driven by a photoinduced phase transition in vanadium dioxide (VO2) forming a three-dimensional photonic crystal. An ultrashort 120-fs laser pulse induces a phase transition in VO2 filling the pores of an artificial silica opal, thus changing the effective dielectric constant of the opal. Consequently, the spectral position of the photonic stop band blue-shifts producing large changes in the reflectivity. The observed switching of the photonic crystal is faster that 350 fs. The demonstrated properties of opal-VO2 composite are relevant for potential applications in all-optical switches, optical memories, low-threshold lasers, and optical computers.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.